My 01 Toyota Sequoia is using Oil.

15 years old - you don't say how many miles and if it is the original engine. We can guess all we want , but to answer accurately you MUST first verify no external oil leaks. IF you find leaks , they should be fixed or else what you THINK is being burned , may very well be leaking. AFTER any leaks are fixed , then it can be scanned/monitored and determine if it is running properly. Leak-down and compression tests can be performed if it is deemed necessary. ALL engines use some oil , some given conditions , will use more. For example , My 1995 Toyota Camry with 393,512 miles on it , burns about 1 quart every 1,000 miles and it leaks about 1/2qt.. On the other hand.......a newer (relatively speaking) Honda Accord, lets say 2013 model (also 4Cyl. for the example) ACCORDING TO HONDA It is acceptable to use up to 1 quart of oil per 1,000 miles driven......sooooo.... but 3 quarts- uh , no , I would have that checked!

Id slow down on this one. So you never had a problem before? Just had the oil changed and now its low. First the dip stick on that vehicle tends to give inaccurate readings usually 1/2 qt, and was it filled properly last service? I would fill the oil and monitor it over the next 1,000 miles to get an idea of the oil consumption. And yes, make sure its not pouring out on the ground. Your 4.7 engine is an amazing engine and I have never repaired one for gross oil consumption.

Perhaps being lost through the water system (like in a blown head gasket) or out a vent?